Selective catalytic reduction (SCR) systems have been used to reduce automotive emissions. However, SCR systems may use a reductant, such as urea, stored in an on-board storage device that may be subject to tampering. For example, a vehicle operator may introduce an ineffective fluid to a reductant storage device.
One way to detect operator tampering attaches a urea concentration sensor to a reductant storage device opening to detect the introduction of a non-urea solution (or reduced-urea solution) fluid. However, urea concentration sensors may increase vehicle cost, and may lead to still further diagnostic issues. Further, the availability of urea concentration sensors may be limited.
The inventors herein have realized that a logic driven method may be implemented using existing system infrastructure to monitor reductant quality of an emission control system by determining a pre-refill operating condition of the emission control system, detecting a refill event of a reductant storage device, after said refill event, determining a post-refill operating condition of the emission control system, comparing said post-refill operating condition to said pre-refill operating condition of the emission control system, and detecting a reduction in reductant quality based on at least said pre-refill and post-refill operating conditions. In another approach, a change of a monitored operating condition can be correlated with a re-fill event to determine whether to indicate a potential for urea storage modification, and/or whether to modify engine or vehicle operating conditions. Such methods of monitoring reductant quality may facilitate the detection of undesirable fluids entry into an emission control system without the installation of additional hardware, or in addition to such hardware.